In many fields, it is necessary to dispense a pre-determined amount of fluid in a short period of time. One such instance is on a production line for machines which require a certain amount of fluid to be added to them as part of the manufacturing process. One example is a production line for refrigerating devices which require an accurately measured amount of fluid refrigerant to be dispensed to the refrigerating device. Such refrigerant is often dispensed at high pressure in order for it to be dispensed in a short period of time. This is required on a production line to permit other manufacturing functions to be completed timely.
Generally, the apparatus presently used to dispense refrigerant is either a pump which dispenses refrigerant from a reservoir to the refrigerating device or, alternatively, a pneumatic ram to force fluid refrigerant into the refrigeration device. It is critical to measure the amount of refrigerant dispensed because a refrigerating device will not function properly if either too much or too little refrigerant is injected into it.
This measurement is currently achieved by a volume or mass flow meter to monitor the rate of dispatch of fluid refrigerant from the high pressure source. However, these flow meters are expensive. A further disadvantage of these flow meters is that they are not always accurate as it is necessary to convert the flow rate into weight to measure the amount of fluid dispensed. As the relationship between volume and weight is temperature dependant, such flow meters must either be calibrated for a standard temperature or must be further fitted with temperature sensors to correct the weight reading. An alternative method used to measure the amount of fluid refrigerant dispensed is to utilise position indicators or stops in conjunction with a ram. This method tends to be less accurate and also suffers from the temperature sensitive nature of the relationship between volume and weight.
In an effort to improve the efficiency and reliability of such fluid dispensing apparatus, investigations have been carried out to develop a fluid dispensing apparatus with a more reliable and/or cheaper and/or simpler means of monitoring the amount of fluid dispensed.
In order to overcome the temperature dependent nature of the means used to measure the amount of fluid dispensed, it was proposed to measure the actual weight of the fluid to be dispensed. However, it was found that the conventional means to dispense fluid, particularly fluid under pressure, were inappropriate for sensitive weight measuring apparatus as they set up significant hammering of fluid, and the inertia of fluid flow and further the average flow rate is too slow for a production line process.